2021年青海玛多MS7.4地震前大武台地电场优势方位角异常特征分析

为了深入了解2021年5月22日青海省玛多M_S7.4地震前是否存在地震电信号，本文利用地电场优势方位角方法对大武地电场的原始资料进行了分析，获得了玛多地震前震中附近场地的岩体裂隙结构变化特征，并结合本次地震震中500 km范围内八个地电场台站的岩体裂隙结构变化和该台记录到的以往震例中大武台地电场优势方位角异常变化与中强地震之间的关系进行了综合分析。结果显示：大武台新旧两套地电场数据的地电场优势方位角在震前11个月出现了显著的同步偏转现象，其中大武旧台在震前两个月优势方位角再次出现大幅度上升，异常特征主要表现为优势方位角出现同步快速偏转，最大偏转达到45°—90°；处于同一次级地块的甘孜台、玛曲台与大武台出现准同步异常现象，而其它次级地块上的台站均无异常出现，表明异常响应受到区域构造的影响。再结合大武台地电场使用该方法分析的以往震例表明：大武台的地电场优势方位角异常在中强地震前具有较好的中短期指示意义。

Characteristics of the dominant azimuth anomalies of geoelectric field at Dawu station before MS7.4 Maduo，Qinghai earthquake in 2021

In order to know whether there were seismic electrical signals before M_S7.4 Maduo, Qinghai earthquake on 22 May 2021, this paper analyzed the original data of geoelectric field from Dawu seismic station by using the dominant azimuth method, and the variation characteristics of rockmass fracture structure before the M_S7.4 Maduo earthquake were obtained. Furthermore, the rockmass frasture structure characteristics of eight geoelectric stations within 500 km of the earthquake and previous related earthquake cases are comprehensively analyzed. The results show that the geoelectric field dominant azimuths of the two observation sites at Dawu had a significantly synchronous deflection phenomenon eleven months before the earthquake, and the geoelectric field of one site increased sharply again one month before the earthquake. The abnormal characteristics of the site are mainly manifested as the rapid deflection of the jump range of the dominant azimuth, with the maximum deflection reaching 45°?90°. Additionally, the stations Garze and Maqu in the same secondary block showed quasisynchronous changes with the Dawu station, while the stations in other secondary blocks showed no anomalies, indicating that the abnormal responses are affected by regional tectonic settings. And combined with the previous earthquake case analyses, it is deduced that the dominant azimuth anomaly based on the Dawu electric field has good prediction efficiency for the short and medium term earthquake.